On the Hunt for Another Earth
By Abel Mendez
Astronomers are making progress in finding planets that broadly resemble our own.
This Article From Issue
July-August 2023
Volume 111, Number 4
Page 242
Extraterrestrial life is a genuine scientific possibility. Earth proves that at least one habitable planet, even a planet with technological intelligence, can exist. Astronomers have discovered more than 5,000 exoplanets—worlds circling other stars—and that number increases weekly. Now the search for habitable worlds is on, pushing our data and models to the limits.
QUICK TAKE
- Potentially habitable planets require rocky surfaces with liquid water and a substantial but not overwhelming—at least, those are requirements for life as we know it.
- No true Earth analog has yet been found, but the author has developed an Earth Similarity Index to identify planets that broadly resemble our own and deserve closer scrutiny.
- Gases associated with life on Earth, such as oxygen alongside methane, could indicate biological activity on another planet. The search for chemical biosignatures is starting now.
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